Method and apparatus for ion pumping and pressure measurement



H. F. WINTERS Dec. 5, 1967 6 Sheets-Sheet 1 Filed July 28, 1965 m 8 W W25% f 1 A. 6 mm ,I/W1\ 5 .44 A. M m m L= m m m I w m R m HU I I I I l l Il ll H. F. WINTERS 3,356,287

1] PUVFH'JG AND PRESSURE MEASUREMENT Dec. 5, 1967 METHOD AND APPARATUSFOR IC 6 Sheets-Sheet 2 Filed July 28, 1965 INVENTOR. HAROLD F. WINTERSFIG. 4.

Dec. 5, 1967 H. F. WINTERS 3,355,237

METHOD AND APPARATUS FOR ION PUMPING AND PRESSURE MEASUREMENT Filed July28, 1965 6 Sheets-Sheet Z INVENTOR. HAROLD F. WINTERS F IG. 5 %AM@4%WMATTORNEYS H. F. WINTERS Dec. 5, 1967 METHOD AND APPARATUS FOR IONPUMPING AND PRESSURE MEASUREMENT Filed July 28, 1965 6 Sheets-SheetINVENTOR.

HAROLD F. WINTERS FIG, IO.

ATTORNEYS H. F. WINTERS Dec. 5, 1967 METHOD AND APPARATUS FOR IONPUMPING AND PRESSURE MEASUREMENT 6 Sheets-Sheet 5 Filed July 28, 1965 mE T MN W W. F D L O R A H H. F. WINTERS Dec. 5, 1967 METHOD ANDAPPARATUS FOR ION PUMPING AND PRESSURE MEASUREIIIENT 6 Sheets-Sheet 6Filed July 28, 1965 F'IG. I5.

HIIIIII FIG. I4.

FIG. I6,

IN VENTOR. HAROLD F. WINTERS ATTORNEYS United States Patent 3,356,287METHOD AND APPARATUS FOR ION PUMPING AND PRESSURE MEASUREMENT Harold F.Winters, San Jose, Calif., assignor to Granville-Phillips Company,Boulder, Colo., a corporation of Washington Filed July 28, 1965, Ser.No. 475,344 37 Claims. (Cl. 23069) ABSTRACT OF THE DISCLOSURE Agetter-ion pump is disclosed wherein a first electrostatic field isestablished between a rod-like anode and a coaxially disposed,cylindrical grid surrounding the anode, the anode being positivelybiased with respect to the grid. A second electrostatic field isestablished between the grid and a coaxial, cylindrical cathodesurrounding the grid, the grid being positively biased with respect tothe cathode. Various embodiments of electron injectors are disclosed forintroducing electrons into the first field region to thereby ionize gasmolecules present in this region. A getter is mounted on the anode andis sublimated by an electron source independent of the above-mentionedelectron injector, the getter material being deposited on the innersurface of the cathode. Ions resulting from gas molecule-electroncollisions are driven towards the cathode by the first electrostaticfluid. Upon entering the second field, they are accelerated to thecathode and buried in the getter. Thus, an effective getter-ion pumpresults. The presence of the second electrostatic field also tends toeliminate the passage of electrons to the cathode thereby increasing thetotal electron path length and permitting the use of the device as apressure measuring instrument which achieves an accurate detection ofthe ion flow to the cathode.

This invention relates to ion pumping and pressure measurement and,moire specifically, to an improved method and apparatus for achieving along total path length for angular momentum trapped, charged particle inan electrostatic field.

In the past decade, significant advances have been made in thetechnology of producing low pressures. One of the most importantdevelopments has been the getter-ion pump which, in many applications,has provde superior to other types such as diffusion pumps or mechanicalpumps employing vanes or impellers.

A getter-ion pump, unlike more conventional pumping devices, has nomoving parts, contains no fluids such as oil or mercury, and does noteject the pumped gases into the outside atmosphere; but instead, itoperates in a manner such that electrons are released from a suitablesource and caused to move in a region Within the pump until they strikegas molecules with sufiicient energy to create ions or are captured onan electrode. The gas ions thus created are accelerated by appropriateelectric fields and collide with suitable surfaces where they becomeburied. Simultaneously, getter material is sputtered, evaporated, orotherwise deposited on certain interior surfaces so that the buried ionsare further covered. The fresh deposit of getter material reacts withchemically active gases such as, for example, 0 N and H withoutrequiring ion formation. The chemical compounds thus formed remaintrapped on the interior surfaces of the pump.

The greater the distance that an electron can be made to travel beforebeing captured on an electrode, the greater the probability that it willsulfer an ionizing collision with a gas molecule which can then beremoved from the system. There have been two distinctly differentapproaches, each with several modifications, taught in 3,356,287Patented Dec. 5, 1967 the prior art as a means for producing the longelectron path lengths necessaryin efficient getter-ion pumping.

The first of these is the so-called Evaporion approach exemplified byU.S. Patents 2,850,225, 2,888,189, and 2,894,679, wherein the ionizingelectrons are passed back and forth through grids. Even a open grid willintercept essentially all of the electrons after only a few dozentra-versals, hence, the resulting electron path is quite short.

The second has become known as the sputter-ion ap proach (U.S. Patent2,993,638) which utilizes magnetic and electric fields to confine theelectrons. These devices are a great improvement over the Evapori-o-ndevices because the electrons do not traverse grids, therefore theyalways circulate in free space. To obtain high pumping speeds, however,multiple cell geometries must be employed and these cells have to beplaced between the pole faces of permanent magnets to obtain therequired strong magnetic fields. Thus, in these devices, it is difficultand costly to maintain high gas conductance to the cells and still getthe cells into the narrow magnet gaps provided by the present-daypermanent magnets. In addition, these magnets are costly, bulky, heavy,and produce unwanted stray fields. Because 'of this tight geometry, itis almost impossible to vaporate getter material uniformly into thedischarge volume to enhance pumping or to cover previously buried ions.Sputtering is used in such devices to provide fresh getter material,but, the sputtering must be so intense that it tends to uncoverpreviously buried gas. A third way of producing long electron pathlengths was suggested by J. R. Pierce in his book, Theory and Design ofElectron Beams (Van Nostrand Co. Inc., New York, 1949), pp. 33-34. Theauthor describes the confinement of electrons by the conservation ofangular momentum in purely electrostatic fields without the use of gridsor magnetic fields. In section 4.2 of Pierces book, Radial ElectricFields; Conservation of Angular Momentum, he writes:

Consider a field in which the potential is a function of radius only.Such a field might be a charge-free field, or it might be one in whichthere is an appreciable charge due to moving electrons (space charge).As F, is zero in such a field, from Suppose, for example, electron-sleave the interior of a cylindrical cathode with initial velocities(perhaps thermal velocities) and are attracted toward a smallcylindrical anode,

Pierce goes on to show that if the electrons are injected with suitableangular momenta they can be made to miss the central anode.

Elementary energy considerations show that if the electrons emerge froma source at a potential intermediate between the cathode and anode, theywill have insufficient energy to reach the cathode. Furthermore, theylack the energy necessary to escape through the ends of the cylindricaldiode regardless of whether end caps are provided on the cathode or not.Thus, the electrons are constrained to circulate continuously about theanode until they either strike the electron source from which theyemerged or suffer a loss in angular momentum because of fieldassymetries or because they have collided with a gas molecule. Gas ionsthus created are accelerated to the cathode by the radial field wherethey are captured as in any getter-ion pump.

It thus becomes apparent that the problem of producing an efficientelectron trapping device incorporating such as arrangement requires thatone devise a method of injecting electrons with a suitable angularmomentum and energy and with the electron injection device so placedthat it does not appreciably disturb the radial field, and thus allowsas many electrons as possible to be trapped.

Prior art U.S. Patent No. 3,118,077, utilizes an electron gun to directa well defined beam of electrons tangentially into the annular spacebetween the cathode and anode, but, such an arrangement suffers fromseveral serious disadvantages. To begin with, the electrons all emergefrom the electron gun with very nearly the same angular momentum andenergy and, hence, follow the same path, except for a slight spacecharge spreading. Also, the entire electron path lies in essentially thesame plane, resulting in all of the electrons being concentrated in avery small volume of the device. This produces a space charge build-upwhich seriously limits the amount of circulating charge which can bestably contained between the anode and cathode. Because the electron gunlies in the plane of the orbiting electrons, they collide with the gunstructure after only a few excursions around the anode.

It has now been found that these and other problems can be eliminated inaccordance with the teaching of the present invention by injecting theelectrons into the annular space between the cathode and anode so thattheir paths essentially fill the space and so that they are urgedaxially away from the emitting source structure. The electrons are allinjected with essentially the same energy but with a continuous range ofangular momenta ranging from values so large that some electrons justmiss collision with the cathode to values so small that a few electronsimmediately collide with the anode. In addition, the electrons areinjected into a region of the electrostatic field Where an axialcomponent of the field exists. Such an axial field component is presentin the region where the anode is terminated short of the cathode orwhere an end cap covers the end of the cathode. Electrons thus injectedtend to orbit about the anode in an infinite number of distinct paths.With each electron acquiring an axial component of velocity, theseelectrons tend to follow rosette-shaped helical orbits away from theemitter source. Hence, with the correct adjustment of the axial velocitycomponent, the injected electrons just miss the injector structure andorbit about the anode as they drift slowly therealong. At the oppositeend of the device from the emitter, the field remains cylindricallysymmetric and the electrons are reflected without net change in theirangular momentum about the anode and drift back along said anode towardthe emitter. Having returned again to the emitter end of the unit, someelectrons will make another similar traverse of the field region. Inthis way the average path length for an electron can be made hundreds orthousands of times longer than the path lengths generated in the priorart devices and the quantity of circulating charge approaches thetheoretical maximum, i.e. the charge on the cylindrical capacitorrepresented by the anode-cathode assembly.

Also, according to the teaching of the instant invention, an open gridelectrode is placed between the cathode and anode, concentric with theanode, and held at a potential intermediate between said anode andcathode. The electrons are injected into the annular space between thegrid electrode and anode with an energy and angular momentumdistribution selected such that the electrons are trapped andconstrained to orbit about the anode. Obviously, the open grid electrodenow functions in the same manner as the cathode in the previouslydescribed diode structure as far as the orbiting electrons areconcerned. The orbiting electrons travel through very long paths and arequite effective in exciting or ionizing gas molecules that are presentbetween the anode and grid electrode. The positive ions created in thismanner are accelerated radially out of the grid-anode region by theelectrostatic field. In addition, they are further accelerated by theelectrostatic field between the grid and cathode to the cathode wherethey are buried. The cathode is made of a gettering material such astitanium, or, preferably, is fabricated from a metal like stainlesssteel onto which is continuously or intermittently evaporated a coatingof getter material.

In the diode structure without the grid, ions formed far from the anodeacquire insufiicient energy to bury themselves in the cathode; however,in the triode device, all of the ions produced in the grid-anode regioncan be accelerated to sufiiciently high energy to bury themselves in thecathode.

Another advantage is realized through the use of the triodeconfiguration. It has been determined experimentally that the electronspace-charge around the anode is unstable at electron densities Whereoperation of the device is efficient. Some electrons are, therefore,able to acquire sutficient additional energy from space-chargeoscillations, collisions, or otherwise to escape to the cathode in thediode device. Thus, the current to the cathode is composed of both ionsand electrons and this net current is not a measure of the gas pressurealone in the diode structure. In the triode device, on the other hand,any electrons which leave the grid-anode region are turned back by theelectrostatic field between the grid and the cathode; therefore, thecurrent to the cathode is composed solely of positive ions and thiscurrent value becomes a true measure of the pressure in the g id-anoderegion, thus enabling the pump to measure the gas pressure within it.

Still another advantage is realized through the use of the triodeconfiguration. By placing the grid closer to the anode, the grid-anodecapacitance is increased with a resulting increase in the electricalcharge stored on the grid-anode capacitor. Hence, the amount of possiblecirculating electron charge is increased with a resulting increase inthe amount of ion production. This result can be achieved withoutdecreasing the cross-section of the cathode and hence Without reducingthe gas conductance into the cathode.

It is, therefore, the principal object of the present invention toprovide a novel and improved method and apparatus for greatly increasingthe total distance and time interval that most electrons travel beforestriking an electrode, the foregoing being accomplished by trapping saidelectrons in purely electrostatic fields established between an elongatecentrally-located anode carrying a positive charge and a secondelectrode charged negatively with respect to the anode positioned incylindrically concentric relation to the latter.

A second objective of the invention herein disclosed and claimed is toprovide an electrostatic field configuration enveloping the anode thatis designed to conserve the angular momentum developed in the electronsthroughout a large portion of their total path.

Another object of the instant invention is the provision of apparatuscapable of introducing electrons into the region surrounding the anodewith sufficient angular momentum to carry them past the latter, yet,with too little energy to reach the negative electrode and, at be sametime, imparting to these same electrons an axial component of velocitywhich will cause them to migrate along the anode.

Still another object of the invention forming the sub ject matter hereofis to provide a device of the character above-described that includes anopen cylindrical grid surrounding the anode, means for accelerating theions radially away from the anode and through the grid, and means forfurther accelerating the positive ions outside the grid.

Yet another objective is the provision of a triode ion pumpconfiguration that has an anode, an open grid electrode surrounding theanode in cylindrically concentric relation to the latter, and a cathodesubstantially enveloping the intermediate grid electrode, the cathode orthird electrode providing means capable of preferentially attractingpositive ions and, preferably, burying them in its surface.

An additional object is to produce a novel and improved getter-ion pumpthat makes use of the triode configuration described above inconjunction with a source of getter material that coats the interiorexposed surfaces of the outermost electrode on either an intermittent orcontinuous basis to provide .a collector for the ions that have beenaccelerated through the grid to the cathode, said cathode surface beingsufiiciently large and so prepared that the getter material will notpeel off.

A further object is to provide a means for evaporating getter materialby mounting the bulk getter material on the anode and bombarding it withelectrons accelerated to the anode.

Still a further object is to utilize the triode configuration as apressure gauge by applying suificient bias between the grid and cathodeto prevent electrons from reaching the latter even though the grid-anodevolume is saturated, and adding means for measuring the current to thecathode which, because it is formed almost entirely of positive ions,provides a close measure of the gas pressure.

Other objects of the present invention are to provide an ion-pumpingapparatus that includes cylindrically symmetric end terminations whichfunction to reflect the electrons with no net change in their angularmomentum, an electron injector located to cause minimal disturbance inthe symmetric potential distribution between the grid and anode whileintroducing the electrons into rosetteshaped helical orbits designed tomiss the injector on their initial excursion around the anode, and anoverall improved geometry wherein a number of factors cooperate toprovide a many-fold increase in ion-pumping speeds without sacrificingactive-gas pumping speed.

Still other objects will be in part apparent and in part pointed outspecifically hereinafter in connection with the description of thedrawings that follows, and in which:

FIGURE 1 is a vertical diametrical section showing the improvedion-pumping apparatus of the present invention incorporating the noveltriode design;

FIGURE 2 is fragmentary section taken along line 22 of FIGURE 1 showingthe details of the electron injector;

FIGURE 3 is a horizontal section taken along line 33 of FIGURE 1;

FIGURE 4 is a horizontal section taken along line 44 of FIGURE 1;

FIGURE 5 is a vertical diametrical section similar to FIGURE 1 butshowing a somewhat simplified diode configuration with a modifiedinjection device that includes a shielded filament which preventselectrons issuing from the emitter from migrating directly to the anode;

FIGURE 6 is a top plan view of the injector structure of FIGURE 5revealing the location ofthe shield in relation to the filament and alsothe concentric grids surrounding the latter;

FIGURE 7 is a diametrical'section taken along line 7--7 of FIGURE 6showing further details of the injector;

FIGURE 8 is a horizontal section taken along line 8-8 of FIGURE 5;

FIGURE 9 is an electrical schematic of the apparatus illustrated inFIGURES 1-4, inclusive;

FIGURE 10 is an electrical schematic of the apparatus of FIGURES 5-8;

FIGURE 11 is a diametrical section of a further modified diode structurewherein the injection device is located near the anode at the extremeend of the cylindrical region into which the electrons are introducedand the opposite end is provided with means for introducing gettermaterial into the apparatus through electron bombardment of a gettersubstance carried on the anode;

FIGURE 12 is a transverse section taken along line 12-12 of FIGURE 11;

FIGURE 13 is an enlarged fragmentary section taken along line 13-43 ofFIGURE 11 showing the particular injector construction;

FIGURE 14 is a vertical diametrical section of a still further modifieddiode structure wherein the injector is moved out onto the periphery ofthe cylindrical region into which the electrons are introduced andtrapped in an electrostatic field;

FIGURE 15 is an enlarged fragmentary half-section taken along line 15-15of FIGURE 14; and,

FIGURE 16 is a fragmentary section taken along line 1616 of FIGURE 15showing the injector details.

Referring now to the drawings for a detailed description of the presentinvention and, initially, to FIGURES 5, 8, 11, 12, 14, and 15, it willbe seen that all of the structures include an elongate rod-likeelectrode 10 mounted coaxially within a second hollow cylindricalelectrode 12. Electrode 10 functions as an anode in each of the severaldifferent embodiments illustrated and a positive potential is impressedthereon as indicated in the schematic electrical diagram of FIGURE 10.

Electrode 12, on the other hand, is biased negatively with respect tothe anode 10 and, for purposes of the present description, willhenceforth be referred to as the cathode.

Now, anode 10 and cathode 12 cooperate with one another to develop apurely electrostatic field therebetween which, in what will be definedherein as its central zone, is substantially radial meaning that theforce field includes no significant axial component. This socalledcentral zone wherein the electrostatic forces are essentially radial andequal at all corresponding radii exists in all the configurations shownat the mid-point of the anode and for some distance on either sidethereof because of the elongate nature of the anode 10. On the otherhand, adjacent the ends of the electrostatic field defined between theseelectrodes, the force field is not all radial, but instead, includes asubstantial axial force component which functions in accordance with theteaching of the instant invention to cause electrons introduced intoeither of these so-called end zones to be accelerated axially along theanode thus resulting in their acquiring an axial component of velocityup and down the anode. The orbital path followed by the electrons aboutthe anode is a rosette-shaped path stretched out along the anode much inthe form of a distorted helix.

The principles relating to conservation of angular momentum of a chargedparticle moving in a cylindrically symmetric electrostatic field arewell-known in the prior art as previously mentioned. As aforesaid, it isonly necessary to introduce these electrons into the electrostatic fieldfrom an emitting surface whose potential is intermediate between theanode 10 and cathode 12 to insure that they will have insufficientenergy to reach the cathode. The other prior art requirement is that thecharged particles be injected into the electrostatic field withsufiicient angular momentum about the anode 10 to carry them past theanode. To accomplish the latter, the prior art teaches the use of anelectron gun capable of focusing the electrons emitted therefrom into awell directed beam. The gun is then located within the electrostaticfield in a position such that the electrons are injected tangentiallywith respect to a surface of revolution developed around the anode asits axis. Significantly, the prior art requires that the gun be locatedin a portion of the electrostatic field where the forces are essentiallyall radially-directed and, furthermore, the guns axis lies in a planenormal to the anode so that the electrons orbit in paths which,likewise, are normal to the anode.

The net result of such a system of electron injection is to producerelatively short path lengths for several reasons. First of all,saturation quickly develops in the portion of the electrostatic fieldwhere the gun is located, whereas, the portions of the field borderingthis saturated volume contain only those electrons which have beenscattered in collisions or deflected there by electron space chargerepulsion. Secondly, practically all the electrons move in a planarorbit which plane contains the electron gun, and after one or moreorbits about the anode the electrons collide with the electron gun.

It has previously been mentioned that one of the prime objectives of theinstant invention is to provide a novel method and apparatus forproducing maximum path lengths and it has been discovered that theteachings of the prior art as set forth above result in foreshortenedrather than lengthened orbital paths. A prime requirement forlengthening the orbital paths followed by the electrons is to providethem with a substantial axial component of velocity. The simplest way ofaccomplishing this desirable end, directly contrary to the teaching ofthe prior art, is to locate the injector at a point in the electrostaticfield where a substantial axial force component is already present,namely, in one of the end zones rather than the central zone and toinject the electrons into a great variety of orbits rather than in awell focused stream or beam. In each of the physical embodimentsillustrated in FIGURES 1, 5, 11 and 14, the electron injection apparatuswhich has been broadly designated by reference numeral 16 will be seento have a substantial portion, and in some instances all, of thefilament 18 displaced axially along the anode so that the electrons willbe emitted therefrom into a region or zone of the electrostatic fieldwhere a substantialy axial force component is present. Theseaxially-directed components of the electrostatic field are largeadjacent the axial extremeties thereof and are zero at or near thecenter. Accordingly, electons injected from the lower end of filament 18in FIGURE 5 will spiral upwardly along the anode following a path havinga greater pitch or inclination relative to a plane normal to the anodethan those injected near the top where the force field is primarilyradial. Thus, with an axially elongated filament such as shown in FIG-URES 5 and 7 where portions thereof lie in the central zone as well asone of the end zones, the electrons follows a wide variety ofrosette-shaped helical orbits along the anode, some having rather tightor compressed paths while others are stretched out and open. The resultis that the entire electrostatic field generated between the electrodesbecomes filled with orbiting electrons which migrate in rosette-typepaths up and down the anode until they strike the injector mechanism or,preferably, a gas molecule with sufiicient energy to ionize same.

Perhaps the simplest apparatus illustrating the fundamentals set forthabove is that shown in FIGURES 14, and 16 to which specific referencewill now be made. The anode 10 comprises a simple elongated metal rodmounted axially inside a cylindrical metal can 12 that serves as thecathode. In the particular form shown, the ends of the can are closed bycircular endplates 20 that include a central opening 22 through whichthe anode passes.

A fiap 24 is released from the cylindrical can wall adjacent the bottomendplate 20 to produce an opening for the injector assembly 16 thatcommunicates the interior thereof. As illustrated, the injectorcomprises a holder 26 that carries electrical leads 28 which supplycurrent to the resistance-heated filament 18 that projects into the canthrough the open flap 24. Mounted ahead of the filament is anaccelerating grid 30 in the form of a shallow cup with a central opening32. Grid 30 is biased by means of lead 34 to draw electrons from theheated filament and impart sufficient angular momentum thereto such thatthe vast majority thereof pass on by the anode without striking it ontheir initial orbit while, at the same time, having insufiicient energyto move out to the cathode. The filament to grid spacing and potentialdifference is chosen to spray electrons in a wide cone out of theinjector. The particular potentials needed at the accelerating grid 30to accomplish the above ends vary with the potentials impressed upon theanode and cathode, the relative positions of the electrodes and injectorassembly, and certain other factors, all of which are known in the artand neednt, for this reason, be discussed in detail.

The specific injector assembly just described sprays electrons out in awide cone. Even those electrons emitted in a plane normal to the anodewill not, as in the prior art units, orbit in planes normal to theanode, but rather, begin immediately to orbit upwardly due to thesubstantial axially-directed force component present in theelectrostatic field in the end zone B thereof. It is important to notethat in this particular configuration the axial component of theelectrostatic field is alone responsible for the spiralling orbitalpaths followed by the electrons and that no axial directivity isimparted thereto by inclining the injector so as to start the electronsout on an upwardly spiralling generally helicoidal path.

Note also that with the electrons being injected with insufiicientenergy to reach the cathode 12, there is very little change of eventhose electrons orbiting quite close to the cathode surface striking theinjector assembly because only the accelerating grid 30 is in positionto be struck and all other elements of the injector assembly are locatedoutside the cylindrical surface constituting the cathode. None of theelectrons will follow orbits normal to the anode such that they couldimpinge upon the injector before completing even a single orbit but manywill pass in close proximity to the injector after having orbited theanode many times and moved up to the top and back down once again.

The distorted helical orbits followed by the electrons are, aspreviously mentioned, rosette-shaped rather than circular as they couldappear if they could be seen looking down into the top of the unit. Fromthe side, on the other hand, they would start out in lower end zone Ewith their orbits spaced rather close together axially but movingprogressively further apart as they approach central zone C where theelectrostatic forces are primarily radial. In this cental zone C theelectrons will travel in orbital paths of essentially constant pitchbecause in central zone C there are essentially no axial forces toaccelerate or decelerate the electron axially. Thus the electronstraverse central zone C with essentially constant axial velocity andfinally arrive at the upper end zone E. In the upper end zone E, they,once again, are acted upon by the axial force component that reversestheir direction of movement along the anode.

It is desirable at this time to discuss the end configurations which arenecessary to produce the required axial electrostatic force componentsthat turn the electrons back into orbits along the anode without lettingthem escape. If the anode is terminated sufficiently short of the openend of the cathode then the electrostatic field has an axial componentwhich prevents electrons from escaping through the open end of thecathode. If the anode terminates near or beyond the end of the cathode,symmetrical end caps are desirable to maintain a cylindrically symmetricend field and to produce an axial retarding field which will preventelectrons from escaping. In the apparatus illustrated in FIGURES 14, 15and 16, fiat circular disks are used at the ends of the cathode can andthese work quite well to deflect the electrons back into the prime forcefield existing in the annular space between the electrodes.

The apparatus of FIGURE 11 uses two different types of endplates 20b and200. One (20b) is solid while the other (200) is of the mesh type.Actually, open meshed endplate 200 is used in this embodiment to providea means capable of passing the gettering material evaporated from source36 thereof onto the interior exposed surfaces of the cathode 12.Endplates 20b and 200 are shaped to provide right-conical surfacesrather than flat ones. Here again, they function quite well to deflectthe orbiting electrons back along the anode because both aresymmetrical.

The remaining end configuration that needs to be described is that ofFIGURE 5 wherein the top endplate is eliminated altogether. The top 42of the hell jar in this particular piece of apparatus could be removedwithout appreciably changing the motion of the electrons. The forcepatterns that are developed at the top end of the electrode are quiteadequate to deflect the electrons back along the anode without anymechanical deflector being required. The baseplate 40 serves to turnback electrons at the lower end of the anode. It can be said, therefore,that if the anode is terminated short of the end of the cathode, nodeflectors are necessary on the ends of the electrodes to develop theaxial force components required to cause the electrons to followgenerally helical orbits up and down the anode; however, if suchdeflectors are employed, they must be symmetrical about the anode astheir reference axis so as not to introduce assymetries into theelectrostatic field.

Before leaving the apparatus of FIGURES 14-16, it should be mentionedthat this assembly is designed to be placed in a vacuum vessel of thegeneral type shown in FIGURES 1 and 5 and which will be described indetail presently. Legs 44 support the unit on the baseplate 40 of thevacuum vessel and the appropriate electrical connections are made toconnectors provided for this purpose in the base.

Next, the attention is directed to the embodiment of FIGURES 11, 12 and13 which includes a few features not present in the device of FIGURES14-16. The conical endplate configuration 20b and 200 has already beendiscussed in suflicient detail and need not be elaborated upon. The bulkgetter material 36 is mounted on the anode and bombarded with electronsfrom a heated filament 38 maintained at cathode potential. Bycontrolling the heating power input to the filament 38, the electroncurrent to the getter material 36 can be accurately controlled and thusthe evaporation of the getter can be accurately controlled. By mountingthe bulk getter material directly on the anode, additional high voltageleads or supports are not required for evaporation of the gettermaterial. Also such a mount provides a central location for the gettermaterial so that the interior of the cathode is reasonably uniformlycoated with evaporated getter material. It should be mentioned thatwhile only FIGURE 11 shows a source of getter material and a source ofelectrons to bombard the latter and continuously or intermittently coatthe cathode surface, all of the other pump mechanisms would also beprovided with a similar system for applying a uniform coating of gettermaterial onto all exposed interior surfaces of the cathode. Obviously,as in FIGURE 11, the source of gettering material must be locatedrelative to the surfaces it is to coat such that a minimum of shadowingoccurs due to the presence of other components that will intercept theevaporated material before it reaches the walls that must be coatedtherewith.

Another difference between the embodiments of FIG- URES 1416 and 11-13lie in the injector apparatus 16. Injector 16a of FIGURES ll-l3 islocated much closer to the anode than to the cathode, the oppositehaving been true of injector 16 in FIGURES l4l6. Injector 16a like 16,however, is positioned at the extreme lower extremity of the apparatusand, in actuality, is located completely outside the main electrostaticfield generated between the anode and cathode. Specifically, theinjector is housed inside a small cylindrical can 46 that surrounds thelower end of the anode rod 10 in coaxial relation thereto and isfastened to the underside of solid conical endplate 2012. This can isopen at the top so that the electrons issuing from filament 18 canspiral up that portion of the anode surrounded by this housing beforeemerging into the lower end zone E of the electrostatic field where asubstantial axial component is present. As before, the filament 18 isconnected to electrical leads 28 which supply current thereto and anaccelerating grid 30a (FIGURE 13) connected to lead 34 is biased to drawthe electrons from the filament and impart sufficient angular momentumthereto so that they will miss the anode on their first pass yet beunable to reach the cathode. As before, the accelerating grid ispositioned to start the electrons out on a path designed to by-pass theanode. Here again the injector permits a broad cone of electrons to beinjected into the region between the anode and the small can portion ofthe cathode 46. In other words, grid 30a allows the electrons drawntherethrough from filament 18 to spray out so that relatively few startout on truly tangential orbits; yet, given sufficient angular momenta,even though some are moving away from the anode and others toward it,relatively few will migrate directly thereto upon leaving the injector.Thus, injector 16a exemplifies the fact that the high degree ofdirectivity and tangential injection called for by the prior art is, infact, unnecessary provided each electron is injected with the requiredangular momentum to swing past the anode without striking it.

In this particular embodiment, once the electrons escape through theopen upper end of can 46, they are free to orbit up and down the anodebetween the endplates 20b and 200 without any danger of striking anobstruction other than a gas molecule because there is no hardwarelocated within the electrostatic field other than the electrodes betweenwhich it is generated and the endcaps. The lower endplate 2011 will, ofcourse, effectively reflect most electrons tending to enter can 46through the top.

One other feature of injector 16a deserves special mention and that isthe upward inclination thereof which imparts an initial axial componentof velocity to the electrons before they enter the electrostatic field.Injector 16 of FIGURES l4l6 was solely dependent upon the axialcomponent of the field which exists in the end zones E to start theelectrons spiralling upwardly along the anode. In FIGURE 11, on theother hand, the axially-directed forces imparted to the electron by theupward tilt of the injector and the axial component of the field areadditive which fact further insures their being able to drift upwardthrough the central zone C to upper end zone B.

As before, the apparatus of FIGURE 11 is intended to be mounted and usedin a vacuum vessel of the general type shown in FIGURES l and 5. Such avessel has been indicated in dotted lines.

Next, with specific reference to FIGURES 5-8 and 10, a somewhatdifferent version of an ion pump incorporating the above-describedprinciples will be set forth in detail. Here the metal bell jar 42constitutes the cathode 12m instead of a separate hollow cylindrical canadapted for insertion into the vacuum vessel as was the case with thepreviously described embodiments. The bell jar 42 has a cylindricalshape as shown and is bordered along its lower edge by an externalflange 48 that bolts to baseplate 40 with a gasket 50 therebetween toproduce an air-tight vessel. As is revealed most clearly in FIGURES 4and 8, the baseplate 40 is provided with two conduits 52 and 54 thatcommunicate with the interior of the vacuum vessel. One of theseconduits is connected to the system containing the gas to be removedwhile the other can be connected to a gauge capable of measuring thepressure in the system. Actually, partial evacuation of the system isusually accomplished initially by a small mechanical pump (not shown)which is then sealed off from the system while further pumping isaccomplished by means of the ion pump.

The particular vacuum vessel shown in FIGURES l, 4, 5 and 8 was designedprimarily for testing different designs, such as those of FIGURES 11 and14, which could merely be placed inside and wired to appropriateterminals. In these tests, conduits 52 and 54 provided the necessarymeans for the initial pump-down of the apparatus and subsequentevaluation of its efliciency. The gas conductivity of such a unit,however leaves much to be desired and, for this reason, would seldom beincorporated into an actual high-vacuum or ultra-high vacuum system.Instead, conduits 52 and 54 would be removed from the base and the topleft completely open with a fiange bordering same that could beconnected into the system in vacuum-tight relation. The pumping capacityof the system would thus be increased many times and not be restrictedby the volume of gas that could pass through the small diameter conduits52 and 54. Of course, vacuum vessels designed to provide highconductance of the type aforementioned are well known in the art, and itis to be understood that they would be employed to the exclusion ofthose vaccum vessels illustrated.

Anode 10 is fastened in coaxial relation to the cathode 12m by connector56 which also fastens to an insulated air-tight electrical mounting postassembly 58 fastened centrally within the baseplate 4t) and providing anexterior conductor 60 by means of which a positive bias can be appliedto the anode through variable DC power supply 62 (FIGURE 10).

The noteworthy differences in the apparatus of FIG- URES -8 are to befound in the injector assembly 1612. Here, filament 18b (FIGURE 7)comprises an elongate straight wire stretched vertically between thefree ends of electrical leads 28 which, as before, supply bias potentialand power thereto from outside DC. power supply 64 and source 96 (FIGURELeads 28 enter the vacuum vessel through other insulated vacuum-tightelectrical posts 66 and 68 having structures identical to post 58 thatcarries the bias current to the anode. One of the leads 28 has areversely-bent end portion 70 at its upper extremity to which thefilament 18b is attached and the other lead fastens to the bottom of thefilament. It is most important to note that filament 18b providesomnidirectional emissions, whereas, the previously-described filaments18 (FIGURES 11-16) were at least somewhat directional due to theplacement and construction of the accelerating grids and 30a. The use ofan omni-directional injector assembly means, of course, that some of theelectrons emitted thereby will migrate directly to the anode because,regardless of their energy, they will have been released withinsufiicient angular momentum to miss the anode. When this occurs, theanode will intercept these electrons after they have traveled throughonly very short paths. Thus, they are not effective in producing ions.These electrons also bombard the anode, heating it and causing it tooutgas, which is undesirable. These nonproductive electrons alsocontribute to the electron space charge between the anode and cathodeand prevent useful electrons from being injected.

Accordingly, it becomes important to shield the anode from the action ofthose electrons which otherwise would migrate directly thereto. Such ashield has been shown at 72 in FIGURE 7 located between the filamentsand anode. That is, the support wire for the upper end of the filamentis interposed directly between the anode 10 and filament 1812 so thatemitted electrons cannot travel directly to the anode.

As was true of the other injectors, the filament 18b has a considerableportion at the lower end thereof displaced axially from the central zoneC of the electrostatic field such that it lies in the lower end zone Bwhere a substantial axial force component exists that will deflect theelectrons upwardly into distorted helical orbits. Obviously, theaxially-directed component acting upon the electrons issuing from thefilament 1812 can be rendered more effective by merely lowering theinjector assembly 161: relative to the anode 10 so as to place more orall of the filament in one of the end zones E.

The injector assembly is located in close proximity to thecathode-forming cylindrical wall of the bell jar. The filament 18b inthis particular injector assembly is surrounded by two coaxial tubularaccelerating grids 74 and 76. The inner accelerating grid 74 issubstantially coextensive in length with the filament 18b and, as shown,is eccentric with respect thereto. The larger of the two grids 76 isalso longer and, as aforesaid, is arranged coaxially with respect to thesmaller grid. It is not necessary for the grids to be of differentlength nor is it necessary for them to be as long as shown.

Both of these grids 74 and 76 are formed by spot welding endless wirehelixes 78 and 80 to the four rod-like supporting members 82 and 84. Oneof the supports (82b and 84b) of each set of four thereof are connectedthrough leads 86 and 88 (FIGURE 7) and through insulated posts 90 and 92(FIGURE 8) in the baseplate to an exterior source of direct current.Specifically, as seen in the circuit diagram of FIGURE 10, small grid 74is connected to receive a positive bias from DC. source 94, the negativeside of which is connected to filament circuit 28 powered by groundedD.C. source 64 and A.C. generator 96. More specifically, as shown inFIGURE 10, grid 74 is biased positively with respect to filament 18b byvirtue of DC. source 94 and filament 18b is biased positively withrespect to ground potential by virtue of DC. source 64. As shown, thefilament is powered by generator 96 which is connected seriallytherewith and is connected to the juncture of the positive and negativeterminals, respectively, of DC. sources 64 and 94. Large grid 76, on theother hand, is biased positively with respect to ground by DC source 98.

Specifically, the potential of outer grid 76 is adjusted so that thegrid 76 is generally somewhat above the local potential in its vicinity.Most electrons emerging from grid 76 thus encounter a potential gradientwhich has a substantial v-directed or transverse component. As theelectrons move down this potential gradient, they acquire a considerableangular momentum which enables them to orbit about the anode for aconsiderable time before being captured thereby. The potential of grid74 and of filament 18b is adjusted to give a suitable electron emissioncurrent and energy.

Now, from an inspection of the apparatus of FIGURE 5 it would appearthat the large injector structure 16b located within the electrostaticfield would introduce substantial asymmetries therein and, mostimportant, provide structures which would intercept many of the orbitingelectrons and thus etfectively reduce the average path length traveledby the electrons. Despite the seeming deficiencies in such anarrangement, it proved to be an excellent piece of equipment and farexceeded the results predicted therefor. For instance, with 3000 voltsimpressed upon the anode and at a pressure of 5 10- Torr, an averageelectron path of 710 cm. was obtained. At a pressure of l l0 Torr, theaverage path length was increased to 1110 cm., the latter figurerepresenting an average path length several hundred times greater thanit is possible to achieve in a Bayard-Alpert gauge tube.

If we define 'y as the product of the path length and the electroncurrent, we have a direct measure of the ion forming ability of thedevice. With an emission of 5 ma. at 5 1O Torr, 7:3550 ma. cm.; and, atp=1 l0 7:5550 ma. cm. These, of course, are extremely large values for'y.

The most elaborate of the several embodiments is that which has beenillustrated in FIGURES l4 and 9 which will now be described. Actually,the apparatus of FIG- URES 58 proved to be the most effective of thoseshown in maximizing the value of 'y, the one illustrated in FIG- URE 1producing an average path length of around 500 cm. and a 'y of 720 ma.cm. at 5 X 10 Torr.

There remain, however, a number of other significant improvementsincorporated into the FIGURE 1 apparatus that are not present in theother embodiments. Note that, once again, the bell jar 42 of the vacuumvessel functions as the cathode 12m, an anode 10 is located on the axisdefined by the cylindrical wall of the bell jar, and electron injectionassembly containing an axially displaced filament is provided within theelectrostatic field generated between the anode and cathode. Inaddition, however, a third electrode 100 is interposed between the anode10 and cathode 12m in circumferential coaxial relation to the formerelectrode. This third electrode afiords a 13 number of distinctadvantages which are not readily apparent.

To begin with, because of the closer proximity of the grid electrode 100to the anode than the proximity of cathode 12m thereto, the capacitancebetween said grid and anode is considerably larger than the capacitancethat would exist in the system if it contained only the anode andcathode without the grid. It follows, therefore, that the electricalcharge that can be stored on the grid-anode capacitor is substantiallygreater than could be stored on the cathode-anode capacitor without thegrid. The circulating electron charge that can orbit in a stablecondition about the anode is limited to approximately 50 to 75% of thebound charge on the capacitor; therefore, it follows that the grid-anodecapacitor offers an opportunity for greatly increasing the number ofcirculating electrons that can orbit the anode with the attendantincrease in ion pumping effect.

Quite obviously, this same increase in ion pumping capacity could berealized by decreasing the diameter of the cathode 12m to that of thegrid electrode 100; however, to do so would bring about a very seriousdecrease in active gas pumping capacity. It is equally obvious that theanode diameter could be increased to increase the capacitance but thiswould seriously decrease the ion pumping effect by shortening theelectron path and could also decrease the gas conductance of the deviceby obstructing the flow path. It must be remembered that a pump of thistype is, in essence, two pumps having different functions and not alwaysconsistent. Specifically, these units must pump the chemically-activegases such as, for example, oxygen, nitrogen and hydrogen; but, inaddition be able to rid the system of the chemically-inactive gases likexenon, krypton, neon, argon and helium. The active gases present noparticular problem as they are readily trapped on a surface coated witha suitable gettering material such as titanium, with which they combinechemically. The atoms of the inactive gases, on the other hand, must beionized by electron bombardment to produce positive ions which can thenbe driven into appropriate collecting surfaces and buried under a layerof freshly deposited getter material.

The inconsistencies arise because of the considerably greater volume ofactive gases that must be handled by the system in comparison to theinactive gases. A pump designed to handle large volumes of active gas,for the reasons aforementioned, will have a small ion pumping capabilitydue to the reduced capacitance of a system having a cathode spaced faraway from the anode. Conversely, an increase in ion pumping capacityresulting from moving the cathode in closer to the anode decreases theactive gas conductance of the cathode as the cube of its diameter. This,obviously, is a serious limitation of the diode-type getter-ion pumps inwhich the solution involves a compromise between the active and inactivegas pumping capacities with both suffering a substantial decrease.

It is now possible through the use of the triode configuration shown inFIGURE 1 to retain the large diameter cathode 12m so necessary to a highactive gas conductance and, at the same time, provide optimum inactivegas pumping capability through the use of high-capacitance grid-anodeconfigurations. In this connection, it is important to point out thatthe radially-symmetric electrostatic field so necessary to theproduction of long average electron paths is achieved by using a hollowcylindrical grid electrode 100..encircling the anode in coaxial relationand is'independent of the shape or location of the cathode relative tosuch a grid-anode system. In other words, while the apparatus of FIGURE1 shows a cylindrical cathode 12m encircling the grid electrode 100 andI plurality of small grid-anode subassemblies could be grouped insidethe cathode 12mand each of these smaller subassemblies would have ahigher capacitance as well as higher ion-pumping capability by reason ofthe close proximity of the grid electrode to the anode. In addition,each of these subassemblies would require its own separate injectorassembly, however, a single source of gettering material like that shownin FIGURE 11 located centrally with respect to the cathode to insure aneven deposition thereof will suffice. As for the cathode 12m, its shapeis immaterial insofar as the ion-pumping and active gas pumpingcapabilities are concerned except that all internal surfaces should opentoward the source of getter material and be in a position to receive afairly uniform coat thereof. An irregular surface would have theadvantage of increased area but suffer from the disadvantages of beingdifficult to coat uniformly, the latter being easily accomplished on acylindrical surface like that shown in FIGURE 1.

Specifically with respect to the apparatus shown in FIGURES 1-4 and 9,the entire vacuum vessel is the same as that previously described. Thegrid-electrode is of the open mesh type and is biased positive withrespect to the cathode 12m which is at ground potential, the latterforming a wall of the vacuum vessel. The grid electrode 100 is connectedas shown in FIGURE 9 to the positive side of DC. power source 94. Thebias current to the grid enters the vacuum vessel through connector 66,fastener 104 and ring 106.

Grid 100 together with end caps 20a form a cylindrical basket havingfiat circular meshed ends. The basket has metal rings 106 at both endsthereof spanned by braces 108 that constitute its frame. Each of therings carries several insulators 110 that hold the cylindrical gridcentered coaxially relative to the anode and in spaced relation to thecathode. Legs 111 having insulators 113 on their lower ends rest on thebaseplate 40 and support the basket up inside the vacuum vessel. Anopening 112 is provided in the bottom endcap 20a sized to pass theinjector. assembly 160 into the region between the grid and anode.Insulators 114 border this opening to keep the injector assembly out ofcontact with bottom endcap 20a and similar insulators 116 keep it fromtouching the grid electrode.

Injector unit 160 is somewhat directional in that filament 180 ismounted within a shield 118 that has a channel-shaped cross sectionopening more or less tangentially although the electrons issuing fromthe filament are, by no means, restricted to a narrow angle of egress.In fact, an examination of FIGURES 3 and 4 will show that the electronsmay assume introductory orbits spread apart at least 120. The importantfact is that inside wall 120 of the shield 118 prevents any electronsfrom migrating directly to the anode as this wall is interposed betweenthe anode and filament. Electrical lead 28 from A.C.

generator 96 enters the vacuum chamber through insulated connector 90and serially connects to the lower end of the filament. The upper end ofthe filament 180 is grounded to the baseplate 40 through shield 118.

A flat open accelerating grid 300 is positioned in front of the filament180 on the open face of the shield 118 from which it is insulated byinsulators 122. Flat acceleratin-g grid 300 has solid plates 124 bothtop and bottom and the lower one attaches to leg 126 that rests on thebaseplate 40 but is insulated therefrom by insulator 128. The biascurrent to the accelerating grid enters the vacuum chamber throughconnector 68 and lead 130 which cooperates with the leg 126 to supportsame.

Finally, with reference to the circuit diagram of FIG- URE 9, it will beseen that filament is biased at ground potential. Grid electrode 100, asalready mentioned, is biased positively with respect to filament 180 byits connection to the positive terminal of DC. source 94, whose negativeterminal is connected to said filament. Likewise, accelerating grid 30cis biased positively with respect to the grid electrode 100 because thelatter is connected to the negative side of DC. source 132 while theformer is wired to the positive side thereof. A still greater positivebias is applied to anode 10 by virtue of its connection to the positiveside of DC. source 102, the negative side being connected to theaccelerating grid 300. Thus, the grid electrode 100 is biased positivelywith respect to the filament 180 which is at ground potential, theaccelerating grid 30c is biased positively with respect to both thefilament and grid electrode, and the anode 10 is biased positively withrespect to all three.

At the risk of some repetition, it is important to observe in FIGURE 1that, once again, filament 18c is displaced axially to place asubstantial portion thereof in lower end zone B where a substantialaxially-directed force component exists that will act upon the electronsand cause them to spiral upwardly along the anode. This same axialdisplacement of the filament relative to the electrostatic fieldgenerated about the anode is common to all of the illustratedembodiments and is directly responsible for the highly desirablerosette-shaped helical orbits so necessary to achieve long electronpaths and efificient ion-pumping.

In closing, a few general observations can be made which will becomemore meaningful in the light of the specific structural embodiments justdescribed. First of all, the preferred method of injecting the electronsinto the electrostatic field is to supply same with varying degrees ofangular momenta and energy so that they will follow different orbitalpaths and avoid a space charge build-up in a relatively small volume. Anomni-directional electron injection apparatus shielded to preventemissions directly to the anode has proven superior to injectors havinga measure of directivity even though slight.

Secondly, a substantial proportion of the electrons should be introducedin one of the end zones of the electrostatic field where substantialaxially-directed forces exist which will start the electrons onspiralling orbits along the anode. Additional axial momenta may beimparted thereto by tilting the injection mechanism so that theelectrons are introduced into the electrostatic field already possessingan axially-directed force vector tending to move them toward the centralzone where the electrostatic forces are nearly all radial. In this sameconnection, reflectors at the ends of the anode-cathode or anode-gridcapacitors are unnecessary provided the anode terminates short of thecathode or grid, if present; however, if reflectors are used in the formof endcaps, they are preferably symmetrical with respect to the anodealthough the caps on each end may be of different shapes.

Third, it is essential that the cathode provide a hollow cylindricalsurface encircling the anode in coaxial relation to the latter when nogrid electrode is used and the same requirements apply to the gridelectrode in the triode configuration. In the latter embodiment, theshape of the cathode becomes of little significance insofar as theion-pumping capabilities are concerned although it should provide asurface suitable to be coated with a getter material. In fact, theanode-grid capacitor neednt be located coaxially within the cathode butmay, if desired, be placed anywhere within the envelope defined by thecathode which, of course, permits the use ofmore than one grid-anodesubcombination to increase the ionpumping capabilities of the apparatusin relation to the active-gas pumping capacity.

To maintain the cylindrical symmetry of the electrostatic field, it isdesirable to keep the injector mechanism as small as possible. There aretwo reasons for this, namely, the hardware itself introduces asymmetriesin the electrostatic field, and, secondly, it provides a physicalstructure that intercepts some of the orbiting electrons thusdiminishing the average path length thereof.

The triode structure offers several other advantages in addition tothose just mentioned. In a diode configura- 16 tion, positive ionsformed at a considerable distance from the anode lack the energynecessary to bury themselves in the wall of the cathode. On the otherhand, in the triode structure, it becomes a simple matter to furtheraccelerate all ions formed in the grid-anode region by means of thesupplemental potential gradient existing between the grid and cathode.

Furthermore, a highly unstable space-charge exists around the anode athigh electron densities and this oscillating space-charge phenomena canimpart sufiicient additional energy to some of the electrons to allowthem to reach the cathode even though their initial energy level is suchthat this should not occur. If one attempts to measure the gas pressureby correlating same to the current to the cathode, such reading will bein error due to the increment of electron current. The triode structureprovides a solution to this problem because the electrostatic fieldbetween the grid and cathode turns back any electrons able to escape thegrid-anode region and the current measured at the cathode thus becomes atrue measure of the gas pressure because this current represents onlypositive ions.

Having thus described the several useful and novel features of theion-pumping method and apparatus of the instant invention, it willbecome immediately apparent that the several worthwhile objectives forwhich they were developed have been achieved. Although but a fewspecific embodiments of the invention have been illustrated anddescribed herein, I realize that other configurations are likely tooccur to those skilled in the art within the broad teaching hereof;hence, it is my intention that the scope of protection afforded herebyshall be limited only insofar as said limitations are expressly setforth in the appended claims.

What is claimed is:

1. An electrostatic electron orbiting device for use in a vacuum vesselhaving a port for the introduction of gas, said device being of the typeincluding an elongate rodlike conductor forming a first electrode, ahollow substantially cylindrical conductor of the open grid typeencircling the first conductor in coaxial relation thereto defining asecond electrode, a source of electrical energy connected to saidelectrodes in a manner to bias the second negatively with respect to thefirst and establish an electrostatic field therebetween, said fieldhaving an elongate central zone intermediate the ends thereof whereinthe electrostatic forces are essentially radially-directed and endregions abutting the central zone that include substantialaxially-directed electrostatic forces of a magnitude capable of movingan electron released therein toward said central zone, a source ofelectrons positioned and adapted to introduce electrons into theelectrostatic field between the electrodes with insufficient initialenergy'to reach the second electrode and with sufficient angularmomentum such that a majority thereof cannot initially reach the firstelectrode, the source of electrons being disposed relative to theelectrostatic field such that a substantial proportion of the electronsemitted thereby are released in one of the end regions where theaxially-directed forces present in said regions will cause saidelectrons to follow rosette-shaped substantially helical orbital pathsalong the first electrode, and a third electrode which surrounds thesecond electrode in radially-spaced relation thereto, said thirdelectrode being connected to the source of electrical energy and biasednegatively with respect to both the first and second electrodes tothereby establish a further electrostatic field between said second andthird electrodes, said further field tending to prevent the flow ofelectrons therethrough to the third electrode.

2. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: the source of electrons is of the omni-directionaltype adapted to emit in all directions, and in Which a shield isinterposed between said source and first electrode capable ofintercepting those electrons which would otherwise strike the latter.

3. A device as in claim 2 where said electron source includes twocoaxial tubular electron accelerating grids disposed around saidfilament.

4. A device as in claim 3 where the inner one of said two grids isbiased positive with respect to said filament by said source ofelectrical energy.

5. A device as in claim 4 where the outer one of said two grids isbiased positive with respect to said inner grid by said source ofelectrical energy.

6. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: the source of electrons includes a filament and agrid, said grid being connected to the source of electrical energy andbiased thereby at a potential negative with respect to the firstelectrode and positive with respect to the second, and said grid beingpositioned relative to the filament such that the electrons emitted fromthe latter are initially directed into random orbital paths that by-passthe first electrode.

7. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: the source of electrons includes a filament and agrid, said grid being connected to the source of electrical energy andbiased thereby at a potential negative with respect to the firstelectrode and positive with respect to the second, and said grid beingpositioned relative to the filament such that the electrons emitted fromthe latter are initially directed into divergent paths orbiting aroundthe first electrode in the same direction while by-passing same.

8. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: the source of electrons includes a filament and agrid, said grid being connected to the source of electrical energy andbiased thereby at a potential negative with respect to the firstelectrode and positive with respect to the second, and said grid beinglocated relative to the filament such that the electrons emitted fromthe latter are supplied by said grid with an initial axially-directedcomponent acting in a direction to supplement the axially-directedforces present in the electrostatic field.

9. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: the source of electrons is displaced axially towardadjacent ends of the electrodes and a substantial portion of said sourceis positioned outside the essentially radially-directed electrostaticfield generated therebetween.

10. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: at least one end of the second electrode is open andthe first electrode terminates short of said open end.

11. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: the source of electrons includes a filament positionedin spaced substantially para lel relation to the first electrode.

12. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: a source of gettering material is mounted on the firstelectrode.

13. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: the third electrode comprises a wall of an air-tightvacuum vessel.

14. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: the bias carried by the third electrode issufiiciently negative compared with the bias on the second electrode toprevent any electrons that have acquired sufficient additional energy toreach said second electrode from reaching the third.

15. The improved electrostatic electron orbiting device as set forth inclaim 1 in which: the interior surface of the third electrode comprisesa gettering material capable of trapping both active gas molecules andpositive ions of inactive gases attracted thereto.

16. The improved electrostatic electron orbiting device as set forth inclaim 12 in which: means for evaporating the gettering material islocated in close proximity thereto, said means comprising a heatedfilament.

17. A device as in claim 1 including means for measuring the flow of ioncurrent to said third electrode.

18. A device as in claim 1 where said source of electrons is positionedat one of the extremities of the device and is located completelyoutside the electrostatic field generated between the said first andsecond electrodes, said electron source imparting an initial axialcomponent of velocity to the electrons before they enter thelastmentioned electrostatic field.

19. A device as in claim 18 where said electron source is housed in acylindrical container that surrounds one of the ends of the said firstelectrode in coaxial relation thereto and is positioned adjacent saidone extremity of the device whereby the injected electrons escapethrough an open end of said container into said electrostatic fieldbetween the first and second electrodes.

20. A device as in claim 1 where said source of electrons is positionedat the side of one end of the portions of said second electrode, saidelectron source spraying said electrons out in a cone from an opening atsaid side.

21. A device as in claim 20 where said electron source includes afilament and a grid, the spacing and the potential between said filamentand said grid causing said cone of electrons to have a substantialwidth.

22. A device as in claim 1 where said source of electrons includes meansfor initially directing said electrons into divergent paths around saidfirst electrode in the same direction.

23. A device as in claim 22 where said source of electrons includes (1)a filament positioned in said electrostatic field between the first andsecond electrodes and in spaced substantially parallel relation to thefirst electrode and (2) a shield having a substantially channelshapedcross-section, said shield surrounding said filament and openingapproximately tangentially to a radial from said first electrode.

24. An electrostatic electron orbiting device comprising:

means for creating a cylindrically symmetrical electrostatic fieldwithin the device;

means for injecting electrons into said electrostatic field withsufiicient angular momentum to maintain them in orbit until they ionizea gas molecule; and

means for creating a second electric field surrounding the first andblocking the passage of electrons having sufiicient energy to escapesaid first electrostatic field.

25. A device as in claim 24 including means for measuring the flow ofsaid ionized gas molecules through said second electrostatic field.

26. The improved method of producing long electron orbital paths in anelectrostatic field formed between an elongate central electrode and acylindrical electrode biased negatively with respect to said centralelectrode and surrounding same in coaxial relation which comprises:discharging electrons into the electrostatic field with sufficientangular momentum to initially by-pass the central electrode and withinsufiicient energy to reach the cylindrical electrode, introducing saidelectrons in an axially-displaced region of said electrostatic fieldwhere the latter includes a substantial axially-directed force componentoperative to circulate said electrons into rosetteshaped generallyhelical orbits along and around said central electrode, and establishinga second electrostatic field surrounding the first which tends to blockthe passage of said electrons through said second field to the thirdelectrode.

27. The improved method for removing inactive gases from a closed systemwhich comprises: establishing a cylindrically-symmetrical electrostaticfield within the system which includes a central zone of primarilyradiallydirected electrostatic forces and end regions having substantialaxially-oriented forces adjoining said central zone, injecting electronsinto an end region of said electrostatic field with sufficient angularmomentum to cause same to 19 enter rosette-shaped generally helicalorbital paths extending axially thereof, establishing a secondelectrostatic field surrounding the first which tends to block thepassage of said electrons through said second field to the thirdelectrode, and collecting the ions produced by collision of the orbitingelectrons with the inactive gas molecules.

28. The improved method for measuring the pressure in a closed systemcontaining both active and inactive gases which comprises: establishinga cylindri-cally symmetrical electrostatic field within the system,injecting electrons into said electrostatic field with sufficientangular momentum to maintain them in orbit therein until they collidewith a gas molecule and ionize same, establishing a second electrostaticfield surrounding the first which tends to block the passage ofelectrons having sufficient energy to escape said first electrostaticfield, and measuring the flow of ions through the second electrostaticfield.

29. The ion pumping apparatus which comprises: an air-tight vacuumvessel having a port therein for the introduction of gas, an elongate,rod-like conductor forming a first electrode, an open grid-type hollowcylindrical conductor encircling the first conductor in coaxial relationthereto defining a second electrode, a source of electrical energyconnected to said electrodes in a manner to bias the second negativelywith respect to the first and establish a first electrostatic fieldtherebetween, electron injecting means positioned and adapted tointroduce electrons into said first electrostatic field between theelectrodes with insufficient initial energy to reach the secondelectrode and with sufficient angular momentum such that the majoritythereof cannot reach the first electrode, and a hollow imperviousconductor forming a third electrode having an interior gettering surfacearranged in circumferentiallyspaced relation around the secondelectrode, said third electrode being connected to the source ofelectrical energy and biased thereby negatively with respect to saidsecond electrode, said first and second electrodes cooperating toestablish a second electrostatic field encircling the first of saidfields, and the bias on said third electrode being selected such as toprevent the entry into said second electrostatic field of electrons thathave acquired sufiicient additional energy to reach said secondelectrode.

30. The ion pumping apparatus as set forth in claim 29 in which: thethird electrode comprises a wall of a vacuum vessel housing the otherelectrodes and the electron injecting means.

31. The ion pumping apparatus as set forth in claim 29 including meansmounted on said first electrode for producing a gettering surface on theinside surface of said third conductor, the third electrode beingprovided with sufficient negative bias relative to the second electrodeto accelerate the ions passing through the latter and bury same in thegettering surface.

32. The ion pumping apparatus as set forth in claim 29 in which: thefirst electrostatic field includes an elongated central zone wherein theelectrostatic forces are primarily radial and end regions adjoining saidcentral zone that include substantial axially-directed electrostaticforces, and in which the means for injecting the electrons is displacedaxially so that a substantial proportion of the electrons emittedthereby are released in one of said end regions.

33. The ion pumping apparatus as set forth in claim 29 in which: thecylindrical surface of the second electrode lies closely adjacent theanode to increase the capacitance of the first electrostatic field andthe resultant ion-pumping capacity, and in which the volume enveloped bythe third electrode is large compared with that enveloped by said secondelectrode so as to provide substantial active gas capacity.

34. The ion pumping apparatus as set forth in claim 29 in which: bothends of the second electrode are cylindrically symmetrical with respectto the first electrode.

35. The ion pumping apparatus as set forth in claim 29 in which: theelectron injecting means includes an omni-directional filament and ashield interposed between said filament and first electrode in positionto prevent electrons from migrating directly to the latter.

36. The ion pumping apparatus as set forth in claim 29 in which: one endof said second electrode is open and shaped cylindrically symmetric withrespect to said first electrode, and in which said first electrodeterminates short of the open end of said second electrode.

37. The ion pumping apparatus as set forth in claim 29 in which: theelectron injecting means includes a filament positioned in spacedsubstantially parallel relation to said first electrode.

References Cited UNITED STATES PATENTS ROBERT M. WALKER, PrimaryExaminer.

1. AN ELECTROSTATIC ELECTRON ORBITING DEVICE FOR USE IN A VACUUM VESSELHAVING A PORT FOR THE INTRODUCTION OF GAS, SAID DEVICE BEING OF THE TYPEINCLUDING, AN ELONGATE RODLIKE CONDUCTOR FORMING A FIRST ELECTRODE, AHOLLOW SUBSTANTIALLY CYLINDRICAL CONDUCTOR OF THE OPEN GRID TYPEENCIRCILING THE FIRST CONDUCTOR IN COAXIAL RELATION THERETO DEFINING ASECOND ELECTRODE, A SOURCE OF ELECTRICAL ENERGY CONNECTED TO SAIDELECTRODES IN A MANNER TO BIAS THE SECOND NEGATIVELY WITH RESPECT TO THEFIRST AND ESTABLISH AN ELECTROSTATIC FIELD THEREBETWEEN, SAID FIELDHAVING AN ELONGATE CENTRAL ZONE INTERMEDIATE THE ENDS THEREOF WHEREINTHE ELECTROSTATIC FORCES ARE ESSENTIALLY RADIALLY-DIRECTED AND ENDREGIONS ABUTTING THE CENTRAL ZONE THAT INCLUDE SUBSTANTIALAXIALLY-DIRECTED ELECTROSTATIC FORCES OF A MAGNITUDE CAPABLE OF MOVINGAN ELECTRON RELEASED THEREIN TOWARD SAID CENTRAL ZONE, A SOURCE OFELECTRONS POSITIONED AND ADAPTED TO INTRODUCE ELECTRONS INTO THEELECTROSTATIC FIELD BETWEEN THE ELECTRODES WITH INSUFFICIENT INITIALENERGY OF REACH THE SECOND ELECTRODE AND WITH SUFFICIENT ANGULARMOMENTUM